1. Field of the Invention
This invention relates to sod harvesters, and in particular to systems for controlling the process of cutting a strip of sod to a desired length and controlling conveyors used in forming the cut sod into a roll.
2. Description of the Related Art
U.S. Patents Nos. Re. 34,827 to Dover and 5,626,195 to Dover et al., disclose sod harvesters having one or more cutting blades for cutting sod from the ground, an inclined conveyor for conveying the sod away from the cutting blade and which functions alone, or with other conveyors to assist informing the sod into a roll, and a sod cut-off mechanism for cutting the strip of sod to a desired length. The sod cut-off mechanism shown in U.S. Pat. No. 5,626,195 comprises a pair of knife blades slidably mounted on support arms and driven downward by the action of sets of springs. The raising and lowering of the knife blades is generally controlled by a rotating cam which is driven by a chain extending around a first sprocket on a common shaft with the cam and around a second sprocket on a shaft of a ground engaging roller. To change the length of sod to be cut by the harvester, a mechanical or physical change must be made to the cut-off system, such as for example replacing the first sprocket on the common shaft with the cam with a sprocket of a different size. Such changes are time consuming to make and generally cannot be made in the field or while the harvester is being utilized to harvest sod.
Another limitation of such prior art sod harvesters is that an operator must continually monitor and manually adjust the speed of the conveyors to try to match the ground speed of the harvester, to ensure that the rolls form properly. The conveyors of such prior art harvesters are typically driven by a hydraulic motor. An operator adjusts the speed of the hydraulic motors manually by adjusting a knob controlling a valve which controls the flow of hydraulic fluid to the motor. Because the speed of the harvester constantly varies during the sod harvesting process, the operator must continually monitor and adjust the speed of the conveyors. If the speed of the conveyors exceeds the harvester ground speed the system for rolling the sod will place the strip of sod under tension and may tear the strips. If the speed of the conveyors is slower than the harvester ground speed, the rolls formed will be too loose and difficult to transport and handle.
What is needed is a sod harvester having a sod-cut off mechanism which can be controlled to selectively change the length of the strips of sod harvested without having to make a mechanical change to the harvester. The control system would also preferably provide for automatic adjustment of the conveyor speeds relative to the ground speed of the harvester.